 /*******************************************************************************
  * Copyright (c) 2000, 2005 IBM Corporation and others.
  * All rights reserved. This program and the accompanying materials
  * are made available under the terms of the Eclipse Public License v1.0
  * which accompanies this distribution, and is available at
  * http://www.eclipse.org/legal/epl-v10.html
  *
  * Contributors:
  * IBM Corporation - initial API and implementation
  *******************************************************************************/
 package org.eclipse.ui.views.framelist;

 import org.eclipse.osgi.util.NLS;
 import org.eclipse.ui.ISharedImages;
 import org.eclipse.ui.PlatformUI;
 import org.eclipse.ui.internal.views.framelist.FrameListMessages;

 /**
  * Generic "Back" action which goes back one frame,
  */
 public class BackAction extends FrameAction {

     /**
      * Constructs a new action for the specified frame list.
      *
      * @param frameList the frame list
      */
     public BackAction(FrameList frameList) {
         super(frameList);
         setText(FrameListMessages.Back_text);
         ISharedImages images = PlatformUI.getWorkbench().getSharedImages();
         setImageDescriptor(images
                 .getImageDescriptor(ISharedImages.IMG_TOOL_BACK));
         setDisabledImageDescriptor(images
                 .getImageDescriptor(ISharedImages.IMG_TOOL_BACK_DISABLED));
         PlatformUI.getWorkbench().getHelpSystem().setHelp(this,
                 IFrameListHelpContextIds.BACK_ACTION);
         update();
     }

     private Frame getPreviousFrame() {
         FrameList list = getFrameList();
         return list.getFrame(list.getCurrentIndex() - 1);
     }

     private String getToolTipText(Frame previousFrame) {
         if (previousFrame != null) {
             String text = previousFrame.getToolTipText();
             if (text != null && text.length() > 0) {
                 return NLS.bind(FrameListMessages.Back_toolTipOneArg, text);
             }
         }
         return FrameListMessages.Back_toolTip;
     }

     /**
      * Calls <code>back()</code> on the frame list.
      */
     public void run() {
         getFrameList().back();
     }

     /**
      * Updates this action's enabled state and tool tip text.
      * This action is enabled only when there is a previous frame in the frame list.
      * The tool tip text is "Back to " plus the tool tip text for the previous frame.
      */
     public void update() {
         super.update();
         Frame previousFrame = getPreviousFrame();
         setEnabled(previousFrame != null);
         setToolTipText(getToolTipText(previousFrame));
     }

 }

